For example, in the industrial field of semiconductors, toxic gases such as silane (SiH4) gas and halogen system (NF3, CIF3, SF6, CHF3, C2F6, CF4 or the like) gas are exhausted in the semiconductor fabrication process and are abated by incineration. Exhaust gases abated by incineration include solid constituents (for example, SiO2) or acidic constituents (HF, HCl or the like) as by-products of the abatement by incineration. The exhaust gases are then cleaned to remove those solid and acidic constituents therefrom. As cleaning approaches, the approaches using a fan scrubber, a spray tower and the like are known.
In those exhaust gas abatement systems adopting the incineration process, a large amount of water is necessary to cool and clean the incinerated gases at high temperatures (for example, 1700° C.). In the event that only industrial water or tap water is used to satisfy the necessity of such a large amount of water to be used, the running cost involved in the supply of cooling and cleaning water is increased, leading to an increase in waste water treatment. To cope with this problem, technologies have been developed in which water is circulated for use and the circulating water is cooled by a heat exchanger where a heat exchange is carried out between the circulating water and a cooling liquid (for example, Japanese Unexamined Patent Publication No. 2008-161861, Japanese Unexamined Patent Publication No. 2009-18290).